A library of recombinant bacteriophage containing the human genome was screened with a probe specific for globin gene sequences. Recombinants that contained either the epsilon, the two gamma, or the 3' half of the beta globin gene along with extensive flanking DNA were identified. The inserted DNA fragments within the clones containing the epsilon and the two gamma genes were found to overlap; thus the linkage of these genes was established. The epsilon gene is 14 kilobases (kb) 5' to the G gamma gene. Hetero-duplexes formed between two recombinants containing either the two gamma genes or the delta and beta genes were examined for homology by electron microscopy. Heteroduplex formation was observed only between the coding sequences of the respective globin genes; the flanking sequences had completely diverged. Moderately repetitive DNA sequences were found at several locations throughout the beta-like globin gene cluster. An unusually long repeated DNA sequence was found 3' to the beta globin gene. Its length, determined by electron microscopy of heteroduplexes formed between recombinants containing different copies of the repeat, was found to be 6.4 kb. Approximately 3000-5000 copies of this repeat are present in the human genome; thus, this family of moderately repetitive DNA sequences represents approximately 0.5-1.0% of the total human genome.